Sensor package

ABSTRACT

A sensor package is disclosed. One embodiment provides a sensor device having a carrier, a semiconductor sensor mounted on the carrier and an active surface. Contact elements are electrically connecting the carrier with the semiconductor sensor. A protective layer made of an inorganic material covers at least the active surface and the contact elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Utility Patent Application is a continuation of U.S. patentapplication Ser. No. 11/828,085, filed Jul. 25, 2007, which isincorporated herein by reference.

BACKGROUND

The invention relates to a sensor device and more particularly to theart of protecting a semiconductor sensor against environmentalinfluences.

Conventionally, semiconductor sensors are mounted in a casing and arecovered by a gel (often referred to as a globe top) which serves as aprotection against water and other chemical media. Typically, relativelylarge amounts of gel are applied in order to guarantee a sufficientresistance against environmental attacks and a long durability. The gelclosure, however, may alter or adversely effect the characteristics ofthe sensor or may cause other undesired effects.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 illustrates a schematic cross-sectional illustration of a sensordevice.

FIG. 2 is a perspective illustration of the sensor device illustrated inFIG. 1.

FIG. 3 illustrates a schematic cross-sectional illustration of anothersensor device.

FIG. 4 illustrates a cross-sectional illustration of a leadframe onwhich semiconductor sensors are mounted in open cavity structures.

FIG. 5 illustrates a schematic diagram of a nozzle plasma generator.

FIG. 6 illustrates schematic diagram of a plasma enhanced chemical vapordeposition system.

FIG. 7 illustrates a flow chart illustrating a first method formanufacturing a sensor device.

FIG. 8 illustrates a flow chart illustrating another method formanufacturing a sensor device.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

Semiconductor sensors described herein may, for example, be designed aspressure sensors, acceleration sensors, rotation sensors or microphones.Such and other sensors typically include a movable member and may beequipped with integrated electronic circuits which, for example, processsignals that are produced or modulated by the movable member. Themovable member may be produced from semiconductor materials and may bean integral part of a semiconductor sensor chip or it may be made ofother materials, such as for example metal or plastics. In theliterature, combinations of mechanical elements and sensors withelectronic circuitry in a semiconductor chip are often referred to as anMEMS (Micro-Electro-Mechanical System). In the following description,semiconductor sensors may also be sensors without a movable member suchas e.g., magnetic or electric field sensors or optical sensors. Thesemiconductor material may be silicon, but it is also possible to useany other semiconductor material such as compound semiconductors, e.g.,III/V semiconductors.

Protective layers as will be described further below are materials whichtypically have a high barrier effect against hydrogen ingress and/or theattack of other chemical media which might result in corrosion ordegradation of sensitive surface structures of the sensor device. By wayof example, the protective layer may include semiconductor oxide and/ormetal oxide materials such as silicate (Si_(y)O_(x)), e.g., SiO₂, orAl₂O₃, B₂O₃, GeO₂, In₂O₃, PbO, Sb₂O₄, Sb₄O₆, SnO, SnO₂, SrO, Te₂O₅,TeO₂, TeO₃, Tl₂O₃ or ZnO.

The layer thickness of the protective layer may be chosen dependent on avariety of parameters such as the layer material, the requiredresistance against chemical attack, the field of application etc. Aminimum thickness of the protective layer may be about 5 or 10 nm.Often, a thickness of less than 400 nm or, more particularly, 100 nm issufficient for achieving the wanted effects such as e.g., a sufficientresistance to corrosion. In other words, the protective layer is a thinsurface coating deposited from the gas phase.

In FIG. 1, a sensor device is represented in cross-section as anexemplary embodiment. The sensor device 100 includes a semiconductorchip 10, an open cavity structure 11, external conductive terminals 12and wire-bonds 22 serving as contact elements for electricallyconnecting the external conductive terminals 12 with the semiconductorchip 10.

The external conductive terminals 12 form part of a leadframe. As knownin the art, a leadframe is a strip-like metal frame which includes anumber of zones where semiconductor chips are to be mounted. At eachsuch zone, a plurality of leads are suspended at the frame and protrudeinto the interior of the frame. During the manufacturing process, theopen cavity structure 11 is molded to the leadframe and the frame isthen cut-off from leads 13. Leads 13 of the leadframe pass through abottom part 16 of the open cavity structure 11 into the interior (i.e.the open cavity) 17 of the open cavity structure 11 and extend thereinto lead-posts 14. The wire-bonds 22 are bonded to the lead-posts 14 byknown techniques such as wedge-bonding or ball-bonding and connect tochip pads 18, which are arranged on the upper surface 19 of thesemiconductor chip 10.

The leads 12, 13, 14 of the leadframe, the wire-bonds 22 and the chippads 18, amongst other materials used in the assembly, may be subject tocorrosion if being unprotected. For instance, the leadframe may be madeof Cu, Ni/NiP, Au, the chip pads 18 may e.g., be made of Al or Pt andthe wire-bonds 22 may e.g., be made of Au, Cu, Al. Further, the uppersurface of the semiconductor chip 10 is usually passivated with aninsulating hard passivation layer (e.g., Si₃N₄) and may represent theactive surface of the sensor chip 10, in which the functional elementsof the sensor are implemented. As already mentioned, these functionalelements (not illustrated) may be movable mechanical members such as amembrane, a tongue or a cantilever, light-sensitive or electric ormagnetic field sensitive structures in combination with integratedcircuitry. As depicted in FIG. 1, all these elements (i.e. thelead-posts 14, the wire-bonds 22, the chip pads 18 and the upper surface19 of the semiconductor chip 10 containing the functional elements) ofthe sensor may partly or completely be coated with a thin barrier layer20. Especially, the mechanically movable members may be coated by thebarrier layer 20. The thickness of the barrier layer 20 may be smallerthan the thickness of any movable member used in the sensor, e.g., amembrane, a tongue or a cantilever. Therefore, the transfer function ofthe sensor is not substantially effected by the barrier layer 20. It isfurther to be noted that the barrier layer 20 may be transparent so thatit does not impede the performance of an optical sensor.

As a result of the protection of the surfaces coated by the barrierlayer 20 in the interior of the open cavity structure 11, it is notnecessary to apply any further protective material such as a gel oranother padding material. In other words, the outer surface of thebarrier layer 20 may remain exposed to the ambience.

The barrier layer 20 may be made of an inorganic material and may coatall exposed surfaces in the interior of the open cavity structure 11,i.e. also the inner surfaces of the side walls 15, the edges and sidefaces of the semiconductor chip 10 and the regions where thesemiconductor chip 10 is fixed to the bottom part 16 of the open cavitystructure 11 by e.g., an adhesive 21.

The inorganic barrier layer 20 may be made of a mineral material such ase.g., silicate or one or more of the aforementioned materials. As willbe explained further below in more detail, the inorganic barrier layer20 may be deposited from a precursor of metal-organic material orsemiconductor-organic material containing the primary metal orsemiconductor material of the barrier layer.

The open cavity structure 11 may be a mold compound made of plastics.For instance, thermosetting or thermoplastic resin materials may beused. There are various possibilities to attach the open cavitystructure 11 to the leadframe (of which two leads 12, 13, 14 aredepicted). Premold structures are molded to the leadframe prior tosubsequent fabrication processes such as die (i.e. chip) attach and diebonding. Such premold structures may be manufactured by using aninjection molding process, in which the leadframe is clamped into aninjection molding tool used in an injection molding machine.Alternatively, it is possible to first carry out the manufacturingprocesses of die attach and wire bonding and then to attach the opencavity structure 11 to the assembly. In both cases, the inorganicbarrier layer 20 is deposited after die attach and die bonding.

It is to be noted that other bonding techniques such as e.g., ribbonbonding or clip bonding may either be used. Further, other metallicmaterials or conductive polymeric materials may be used for the contactelements within the open cavity structure 11. Further, it is to be notedthat the leads 12, 13, 14 may be of any desired shape and may e.g., passinto the open cavity structure 11 by protruding through the side walls15 rather than through the bottom part 16 of the open cavity structure11.

FIG. 2 illustrates a perspective representation the outer appearance ofthe sensor device 100 illustrated in FIG. 1. In this example, the opencavity structure 11 is a DSOF (Dual Small Outline Flat), SMD (SurfaceMounted Device) housing which is closed by a cap 30. The cap 30 issnapped into place by locking mechanism or locking means 31 interactingwith the open cavity structure 11 and may include an opening 32. Here,the sensor is developed for measurement of barometric air pressure(BAP), but similar packages can also be used for any of the sensor typesmentioned further above.

Usual dimensions of the semiconductor device 100 are a few up to tens ofmillimeters in all three dimensions. By way of example, a DSOF-8-12package has a footprint of 8.6×7.0 mm and a height of 2.8 mm.

FIG. 3 illustrates a further embodiment, in which like parts are denotedby the same reference signs. In the sensor device 200, the semiconductorchip 10 is mounted in a face-down-orientation on a substrate 50 whichforms the bottom part of the semiconductor device 200. In such flip-chiptype package, the active surface 19 of the semiconductor chip 10 facesthe substrate 50. An opening (not illustrated) may be formed in thesubstrate 50 to expose the active surface 19 to an external action to bemeasured such as e.g., barometric pressure, sonic vibrations or light.Solder balls 51 are applied in a peripheral region to the active surface19 of the semiconductor chip 10 and serve as contact elements toelectrically connect the substrate 50 to the semiconductor chip 10.Further, solder balls 52 or other contact elements may be attached tothe outer surface of the substrate 50 and are interconnected with thechip solder balls 51 by an internal metallic redistribution layer notillustrated in FIG. 3.

Similar to the first embodiment, all exposed surfaces in the interior ofthe open cavity structure 11 may be coated with the inorganic barrierlayer 20. By using techniques which will be explained in more detailbelow, it is possible to also apply the inorganic barrier layer 20 tosurfaces located between the semiconductor chip 10 and the substrate 50,e.g., to the active surface 19 of the semiconductor chip 10, to thesurface of solder balls 51 and to metallizations such as chip pads (notillustrated) and corresponding contact areas on the inner surface of thesubstrate 50.

Various methods may be used for depositing the inorganic barrier layer20, including CVD (Chemical Vapor Deposition) and PVD (Physical VaporDeposition) techniques, e.g., sputtering, thermal evaporation, laserdeposition, cathodic arc deposition. As a first example, a plasma nozzlemethod will be described. In this method, the inorganic barrier layer 20is deposited from a gas phase onto the exposed surfaces by a sprayprocess as illustrated in FIG. 4. To this end, a plasma generator 300 ismoved over a continuous, strip-like leadframe with attached open cavitystructures 11 and mounted semiconductor chips 10. Here, the lengthextension of the leadframe is in Y direction and the width of theleadframe is in X direction indicated by arrow 301—i.e. twosemiconductor chips 10 may be mounted next to one another on theleadframe. The plasma generator 300 discharges a plasma 302 which isdirected to the interior 17 of the open cavity structure 11. It is to benoted that the plasma treatment of the sensor devices 100 also providesfor an initial cleaning of the surfaces to be coated. In order to arriveat a sufficient thickness of the inorganic barrier layer 20, the plasmagenerator 300 may perform several sweeping movements in transversal Xdirection (which is perpendicular to the longitudinal Y direction).Thus, the surfaces to be coated are exposed to the plasma beam 302 forseveral times. In order to avoid the exposure of surfaces to the plasmabeam 302 which are not intended to be coated with the inorganic barrierlayer 20, mask plates 303 may be used. In the example illustrated inFIG. 4, the upper surfaces of the external conductive terminals 12 whichproject beyond the outline of the open cavity structure 11 shall not becoated and are therefore protected by the mask plates 303. Such maskplates 303 may also be useful to protect areas of the sensor device 100which are short distant to the plasma generator 300 and thus moreexposed to heat from the plasma beam 302, especially if the plasmagenerator 300 is configured as a blow pipe operable to be used as aflame pyrolysis plasma generator 300.

Virtually all known methods may be used for plasma generation. Morespecifically, plasma generation in the plasma generator 300 may e.g., beeffected by a pyrolysis method, by a method based on electrical and/ormagnetical fields such as microwave or by a method based on laserdissociation. The plasma generator 300 may be designed to generate anatmosphere plasma or a low pressure plasma.

According to FIG. 5, by way of example, a plasma generator 300 mayinclude a metal enclosure 310 connected to a first potential (e.g.,ground), a housing 311 made of an insulating material and an electrode312 connected to a second potential V. Feed-through inlets 313 leadingto an ionization chamber 314 are provided to feed ionization gas into anionization chamber defined by the insulating housing 311 and the metalenvelope 310. Opposite to the electrode 312, the metal envelope 310 hasa tapered shape and ends into a nozzle 315. An inlet 316 to the nozzle315 is connected to a vaporizer or mixer 317. The vaporizer or mixer 317receives a carrier gas through line 318 and a precursor through line319.

The plasma generator 300 illustrated in FIG. 5 may be configured togenerate an atmosphere plasma which is induced by an alternatingelectrical field. Other types of plasma generation which may be utilizedin the plasma generator 300 are flame pyrolysis plasma generation,magnetic field plasma generation, laser beam plasma generation,microwave plasma generation etc. In all cases, a nozzle type atmosphereplasma spray generator similar to that illustrated in FIG. 5 may beemployed. No airtight setup casing is needed if an atmosphere plasmageneration method is used.

According to FIG. 6, the inorganic barrier layer 20 may also bedeposited in a low pressure plasma process. By way of example, anapparatus 400 for generating a low pressure plasma is illustratedschematically in FIG. 6. The apparatus 400 includes a chamber 401 havinga gas inlet 402 and a gas outlet 403. A power supply 404 is connected toan upper electrode (e.g., a showerhead anode) 405 of the apparatus 400.A lower electrode (cathode) 406 is arranged opposite to the upperelectrode 405 and may be provided with a cooling well 407. A powersupply 408 is coupled to the lower anode 406. A strip-like leadframe 409such as depicted in FIG. 4 is transported by using a wheel-to-wheelprocess through the gap between the two electrodes 405, 406.

Apparatus 400 may be designed as a PECVD (Plasma Enhanced Chemical VaporDeposition) system. Similar to atmosphere plasma generation, e.g.,electric fields, magnetic fields, microwave or light may be used forplasma generation. The precursor along with possibly other gaseouscomponents such as for instance a carrier gas are supplied through theinlet 402 and discharged at the outlet 403. The pressure used in thechamber 401 depends on various parameters such as the plasma generationmethod, the desired barrier layer thickness and so on and may typicallybe within the range of 0.1 mbar to one or several mbar. A similarapparatus may be used when a PVD method for depositing the barrier layer20 is employed.

Further, it is to be noted that several modifications to the apparatus400 designed for low pressure deposition are possible. Instead of thewheel-to-wheel method, a batch process may be used, in which a magazinecontaining a plurality of sensor devices 110, 200 (which may already beseparated or still be interconnected) is put on the lower electrode 406and subjected to the low pressure plasma. After processing of onemagazine, the chamber 401 is opened, the processed magazine is removed,a magazine with unprocessed sensor devices 110, 20 is inserted and thevacuum is re-established in order to resume the deposition process.

In both the atmosphere plasma and low pressure plasma CVD processesdescribed before, an organometallic or organic semiconductor ororganometallic semiconductor material may be used as a precursor forbarrier layer deposition. By way of example, the following monomers maybe applied. Commonly used short term designations are added in brackets:C₆H₁₈OSi₂ (HMDSO), C₈H₂₀O₄Si (TEOS), C₄H₁₂Si (TMS), C₄H₁₂OSi₂ (TMDS),C₅H₁₂Osi (TMES), C₆H₁₈Si₂ (HMDS), C₇H₁₈O₃Si (MTES), C₄H₁₂O₃Si (MTMS),C₅H₁₂O₃Si (VTMS), Si(OCH₃)₂(CH₃)₂ (DMDMOS), CH₃Osi(CH₃)₃ (TMMOS) andCH₃Si(OCH₃)₃ (MTMOS).

FIG. 7 illustrates basic method processes used for manufacturingembodiments of a sensor device. In S1, the semiconductor sensor ismounted onto a carrier. As already mentioned, the mounting may includedie attach and bonding. Bonding may e.g., be accomplished by one of theaforementioned bonding techniques.

Then, in S2, the barrier layer 20 is deposited from a gas phase onto thesemiconductor sensor. Although thin, the barrier layer 20 may serve asan unique protection covering for instance all exposed surfaces withinthe interior 17 of the open cavity structure 11, resulting in that anyother protective materials may not be needed.

According to FIG. 8, in S10 a strip-like leadframe is provided. Then,the semiconductor sensor, e.g., semiconductor chip 10, is mounted on theleadframe, cf. S11. Typically, not only one but a plurality ofsemiconductor sensors are mounted. An open cavity mold structure isattached to the leadframe such that the semiconductor sensor is locatedwithin the open cavity according to S12. Again, typically eachsemiconductor sensor is accommodated in such open cavity structure. S12may be accomplished before or after S11. Then, the barrier layer 20 isdeposited from a gas phase onto the semiconductor sensor(s) (S13).

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A semiconductor package comprising: a carrier; asemiconductor sensor coupled to the carrier; and a protective layer madeof an oxide material covering at least a portion of the semiconductorsensor, the semiconductor sensor disposed within an interior of anunfilled open cavity structure, the semiconductor sensor and walls ofthe interior of open cavity structured covered with only the protectivelayer such that all portion of an exterior surface of the protectivelayer are exposed.
 2. The package of claim 1, wherein the protectivelayer is made of a metal oxide.
 3. The package of claim 1, wherein theprotective layer is made of a compound of oxide materials.
 4. Thepackage of claim 1, wherein the protective layer has a thickness in therange of 5 nm to 400 nm.
 5. The package of claim 1, comprising: amechanism that electrically couples the semiconductor sensor to thecarrier; and where the protective layer covers at least a portion of thesemiconductor sensor and the mechanism.
 6. The package of claim 5, wherethe mechanism includes a wire bond.
 7. The package of claim 5, where themechanism includes a solder ball.
 8. A semiconductor device comprising:a carrier; a semiconductor sensor comprising a bottom side and a sidewall adjoining the bottom side, the semiconductor sensor coupled to thecarrier such that the bottom side faces the carrier; wire-bondselectrically connecting the carrier with the semiconductor sensor; aprotective layer made of organic semiconductor material including anoxide, covering at least a portion of the semiconductor sensor anddirectly contacting the wire-bonds and covering and in direct contactwith side walls of the semiconductor sensor, and where the protectivelayer has a thickness in the range of 5 nm to 400 nm, wherein allportions of an exterior surface of the protective layer are exposed. 9.The device of claim 8, wherein the organic material is an organometallicmaterial.
 10. A sensor device, comprising: a carrier; a semiconductorsensor mounted on the carrier and having an active surface and a sidewall; contact elements electrically connecting the carrier with thesemiconductor sensor; a protective layer made of an oxide materialcovering the active surface and directly contacting the contactelements, and covering and in direct contact with the side wall of thesemiconductor sensor where the protective layer has a thickness in therange of 5 nm to 400 nm, wherein all portions of an exterior surface ofthe protective layer are exposed.
 11. The sensor device of claim 10,wherein the protective layer further covers conductive contact elementsof the carrier.
 12. The sensor device of claim 10, wherein the activesurface of the semiconductor sensor comprises a movable member.
 13. Thesensor device of claim 12, wherein the movable member is a membrane or atongue or a cantilever.
 14. The sensor device of claim 12, wherein theprotective layer is thinner than the movable member.
 15. The sensordevice of claim 10, wherein the semiconductor sensor is one of the groupof pressure sensor, microphone and acceleration sensor.
 16. The sensordevice of claim 10, wherein the protective layer has a thickness in therange of 10 nm to 100 nm.
 17. The sensor device of claim 10, wherein theprotective layer is made of a metal oxide or a compound of the oxides.18. The sensor device of claim 10, wherein the protective layer is madeof a silicate.
 19. The sensor device of claim 10, further comprising: anopen cavity structure attached to the carrier, wherein the semiconductorsensor is arranged within the open cavity structure.